A review and new descriptions of Elk Point Group outcrops in the Athabasca Oil Sands mining region

Abstract Elk Point Group outcrops in the Athabasca Oil Sands mining region (AOSMR) and adjacent areas include exposures of the La Loche, Contact Rapids, Keg River, and Prairie Evaporite formations. Here, we review prior investigations of these formations in outcrop, followed by new descriptions of some outcrops, including those previously unpublished or newly discovered. The fluvial to marginal marine sandstone and conglomerate of the La Loche Formation, informally known as the granite wash, outcrops along the Clearwater River in Saskatchewan, where it is sandwiched between the Precambrian basement and the Contact Rapids Formation. In Alberta, the La Loche Formation is exposed at a locality along Whitemud Falls, where it directly underlies the Keg River Formation as a lithic sandstone and fills paleokarst crevices in the Keg River dolostone. From these two outcrops we recognize three facies in the La Loche Formation: regolith, lithic conglomerate, and lithic to arkosic sandstone. The marginal marine shale, silt, and dolomite of the Contact Rapids Formation outcrops in Saskatchewan at its namesake Contact Rapids, but is exposed only as a slumped bank of grey to greenish mud. We examined Keg River Formation dolostone from three outcrops along the Clearwater River at Contact Rapids in Saskatchewan and Whitemud Falls and Cascade Rapids in Alberta. We also describe an outcrop on the Firebag River in Alberta. From these outcrops, we recognize three general facies: bedded to laminated cryptalgal dolomitized bindstone (originating from an intertidal paleoenvironment), coral and stromatoporoid-bearing dolomitized floatstone to rudstone (originally a reef), and crinoid and brachiopod dolomitized floatstone (from off-reef or inter-reef areas). A newly recognized outcrop of the collapse residue from the dissolved Prairie Evaporite Formation occurs along the Clearwater River, where cobbles and boulders of breccia and other less soluble Prairie Evaporite rock weather out of the river bank between several sulfur springs.